Technical Guide
Waterproofing Water Tank
Water Tanks or storage Reservoirs (as they are known when they are large in capacity), are specially designed structures to store water from which supplies are made to the surrounding localities. Leakages and deterioration of many tanks have taken place over the years. Many of them need restoration.
Repairs to existing tanks.
A detailed procedure for repairs to a water tank is provided for guidance.
The following steps have to be taken:
1. Surface preparation
2. Anti corrosive Treatment
3. Steel Strengthening
4. Repairing damaged patches
5. Curing
6. Grouting any voids in concrete
7. Restoration of wall surfaces.
Specification for Concrete Repairs.
Surface Preparation
Surface preparation is of prime importance in any repair work. The success of the repair work depends upon this to a large extent.
I. Chip off all loose concrete and remove the damaged concrete by using a chisel and hammer or other suitable mechanical means.
II. The presence of any delamination should be detected by sounding the vertical (or other) surfaces of concrete on a regular pattern, using a small hammer. The areas should be marked out.
III. After the whole area has been covered remove the damaged concrete from the delaminated areas, till sound concrete is seen.
IV. Expose the reinforcement in all damaged areas using steel wire brushes, normally or mechanically. There should be at least 6mm gap behind reinforcement to facilitate cleaning, coating etc.
ANTI-CORROSIVE TREATMENT & STEEL FOR STRENGTHENING.
V. Apply a suitable rust removal compound as per manufacturer's specifications. Clean the reinforcement so that it shines uniformly.
VI. Wherever the reinforcement is reduced by more than 20 % of the original area, extra new main steel is to be provided by welding it to the existing steel or suitable lap (40 d). In case of columns and beams, provide welded wire mesh (4" X4" X 10 guage) along with two layers of woven GI wire square mesh (½ X ½ X 19 guage) so that the repair material is properly tied up with the sound core. The mesh is to be clamped on to the concrete surface by means of plumber nails and building wire.
VII. Apply a suitable corrosion inhibitor to the old and all new reinforcements.
REPAIRS: METHODOLOGY
VIII. Provide a suitable bonding coat over the reinforcement and concrete surfaces, which is to receive the repair material. Follow the bonding material manufacturer's specifications.
MORTAR & FINISHING
IX. Using polymer modified cement mortar (PMCM) fill up the area to be repaired, with aid of jacked up floating shuttering. The render of the PCMC should be done in layers of 15 mm, (the min being) minimum and at least two coats are to be provided. The material should be evenly applied and well compacted and finished using a wooden float or steel trowel.
CURING
X. Cure the PMCM as per manufacturer's instructions.
GROUTING VOIDS
XI. In case the original concrete is suspect or found to be honey combed or
has internal voids, it may be necessary to grout the concrete. This may be done by drilling holes of 16 mm diameter upto at least 100 mm in concrete to receive the nipples and grouting.
Use a polymer-cement grout as per the manufacturer's specifications.
Note:
Please refer to Technical guide no 7 for details of various repair formulations of Concrete Practice.